DBZ Earth (with some help) vs Reaper Invasion (Mass Effect)
So say Trunks comes back from the future to inform our heroes that in 3 years a threat will come to wipe out the earth unlike any foe they've ever encountered. The Z-Fighters hear this and again prepare for the dark threat that looms over them!
DBZ Earth (End of DBZ levels)
vs
Reapers
Lets say Future Trunks stopped Sovereign in his time (assume Commander Shepherd was there also...and died of a heart virus soon after) and so the info we basically had on the Reapers from Mass Effect 1-2 the Z fighters will have it so they can kind of understand what they're up against. Also Frieza's somehow heard about the looming threat and wants earth for himself but for now agrees to work with the others so they have all of his resources as well with his Brother and Father (Their resources included of course.), this applies to Dr. Gero (Androids and all) as well.
Bulma and Dr. Gero have been looking over the information Trunks brought back and they've developed a way for them to breathe in space while also being able to resist some of the influence of the reapers.
The kais have gave Goku the Potara earings if he needs Vegetto again
Goten and Trunks stand ready as SS3Gotenks
Oh and Hercule somehow got the army into this too so the DBZ world military is offering their assistance along with Mr. Buu
Everyone's been training and has a pouch of Senzu beans how do our warriors fair? With the combined prep and might of the DBZ world can they fight off annihilation, or do the Reapers leave them as a forgotten race like all the rest?